Off-highway vehicles (OHVs), such as railway locomotives, mining trucks, and excavators, may be utilized to move a payload from one location to a different location. It may be desirable to increase the top speed of the off-highway vehicle to increase the productivity of the vehicle as measured by payload moved per unit time. One embodiment of an off-highway vehicle includes a diesel-electric power source coupled to a traction motor coupled to a wheel of the off-highway vehicle. The traction motor applies torque to the wheel so the vehicle speed may be increased as the speed of the traction motor is increased. In one embodiment of a traction motor, the traction motor is an alternating current (AC) induction motor including a stator and a rotor. The stator includes field windings that set up a rotating magnetic field around the rotor, causing the rotor to rotate around an axis. The rotor includes a shaft along the axis, a plurality of conductive bars substantially parallel to the axis, and a pair of end rings for connecting the plurality of conductive bars at each end of the rotor.
During operation of the traction motor, the end rings of the rotor are subjected to a variety of stresses, with some of the stresses increasing as the rotational speed of the rotor increases. Over time, the stresses may fatigue the end rings of the rotor and the rotor may fail, causing down-time and lost productivity for the vehicle. The fatigue may be reduced and the mean time between failures of the rotor may be increased by reducing the peak stress of the end ring, such as by operating the traction motor at a speed below a threshold speed, for example. However, reducing the operating speed leads to still other disadvantages, especially with regard to OHVs where increased speeds are increasingly being demanded.